Fibre-optic cables are rapidly gaining in preference over metallic wire electrical cables for a variety of reasons, especially the wide band width and low attenuation which are characteristic of optical fibres. Optical fibres, however, are generally very thin and unable to withstand appreciable mechanical loading, and thus do not aid in strengthening the cable as do the metallic wires of electric wire cables. As a result, special measures must be taken to reinforce fibre-optic cable because the transmission capability of optical fibres deteriorates as the fibres are subjected to strain. Below a certain level of strain, the deterioration is reversible and it is thus permissible during cable installation to subject the fibre to a moderate strain. The cable must not be subject to even this moderate level of strain during operation. Above that level of strain, however, the deterioration is permanent and is thus not permissible at any stage of handling operation. Thus, it is critical that stresses incurred during handling and operation be prevented from excessively straining the optical fibre.
Various constructions of cable have been proposed which incorporate strength members to reinforce the cable. These constructions include strength members made of metal, pultruded glass rods, polyesters, polyamides, including the wholly aromatic polyamide, p-phenylene terephthalamide. Such constructions have presented one or more disadvantages such as difficulty in fabrication, the presence of an electrically conductive component in the cable, undesirable thermal expansion and contraction under extreme temperature variations and excessive weight and cross-sectional area of the cable. It has been proposed in European patent application No. 83301724.7 (U.S. Ser. Nos. 364,823 and 364,824) to overcome these problems by providing a stiffening support in the cable made from a thermotropic liquid crystalline polymer. The present invention is a development of such use of thermotropic polymers in optical fibre cable.